Characterization of Resistance Gene Analog Polymorphisms in sugarcane cultivars with varying levels of red rot resistance

Resistance Gene Analog (RGA) strategy is being exploited perfectly for the identification, tagging and mapping of major genes or Quantitative Trait Loci for disease resistance. About 29 RGA primers designed from the conserved domains of resistance proteins, were used to analyse the genetic diversity among the 40 sugarcane cultivars that vary in their resistance to red rot disease. The genetic similarity values ranged from 58.4 - 90% with the mean genetic similarity of 74.2%. Cluster analysis resulted in a dendrogram with 3 major clusters and a clear distinction of resistant and susceptible varieties was observed. A total of 25 specific fragments amplified by 14 primers were identified to be associated with resistance and 8 specific fragments amplified by 8 primers were associated with susceptibility. The primers RGA – 137, RGA 396, RGA- 231 and RGA-118 amplified maximum number of resistant or susceptible specific fragments (3). Amplification of the red rot resistant variety Bo 91 and the red rot susceptible variety CoC 671 with the twenty nine RGA primers, followed by sequencing and homology analysis revealed significant homologies with the RGA’s of rice, maize and sugarcane. These RGA’s that were found to be associated with red rot resistant/ susceptible varieties are a valuable source of markers that can be tested for screening red rot resistance in breeding programs.